System and method for carbon dioxide capture and sequestration from relatively high concentration co2 mixtures

ABSTRACT

A system and method of reducing the net carbon dioxide footprint of an industrial process that generates power from the combustion of hydrocarbon fuels in which ambient air is admixed with up to 50% by volume of an effluent gas from the power generator of the industrial process, in order to substantially increase the CO 2  concentration in the air prior to treatment. The treatment comprises adsorbing CO 2  from the admixed ambient air utilizing a cooled, porous substrate-supported amine adsorbent, wherein the porous substrate initially contacts the mixed ambient air containing condensed water in its pores, which act as an intrinsic coolant with respect to the exothermic heat generated by the adsorption process. In addition, prior to regenerating the supported adsorbent, air pressure is substantially reduced in the sealed regeneration chamber and the low pressure chamber is placed in fluid connection with a higher pressure regeneration chamber containing steam and carbon dioxide, to preheat the sorbent to be regenerated and to quickly cool the regenerated sorbent prior to use for further CO 2  adsorption.

The application claims the benefit or priority pursuant to 35 U.S.C.119(e) from a U.S. Provisional Patent Application having Application No.61/643,103 filed Apr. 30, 2010; from a U.S. Provisional PatentApplication having Application No. 61/330,108 filed Apr. 30, 2010; froma U.S. Provisional Patent Application having Application No. 61/351,216filed Jun. 3, 2010 and from a U.S. Provisional Patent Application havingApplication No. 61/443,061 filed Feb. 15, 2011, and from copending U.S.application Ser. No. 13/098,370, filed on Apr. 29, 2011.

BACKGROUND

The present invention relates to systems and methods for removinggreenhouse gases from the atmosphere, and in particular to systems andmethods for removing carbon dioxide from a stream of gas, includingambient air.

As a further improvement to the system described in copending U.S.application Ser. No. 13/098,370, filed on Apr. 29, 2011, a suitablesystem and process is presented that it is now recognized can beutilized for a broader range of use than disclosed in that earlierapplication, especially when further modified. The disclosure of thatcopending application is incorporated by reference herein as if repeatedin full, as modified by the new disclosure presented herein.

There is much attention currently focused on trying to achieve threesomewhat conflicting energy related objectives: 1) provide affordableenergy for economic development; 2) achieve energy security; and 3)avoid the destructive climate change caused by global warming. However,there is no feasible way to avoid using fossil fuels during the rest ofthis century if we are to have the energy needed for economic prosperityand avoid energy shortfalls that could lead to conflict.

It is mostly undisputed by scientists that an increase in the amount ofso-called greenhouse gases like carbon dioxide (methane and water vaporare the other major greenhouse gases) will increase the averagetemperature of the planet.

It is also clear that there is no solution that only reduces the ongoinghuman contributions to carbon dioxide emissions that can successfullyremove the risk of climate change. Removing additional CO₂ from theatmosphere is also necessary. With air extraction and the capability toincrease or decrease the amount of carbon dioxide in the atmosphere, onecan in principle compensate for other greenhouse gases like methane(both naturally occurring and from human activity) that can increasetheir concentrations and cause climate change.

Until the recent inventions by the present applicant, it was thegenerally accepted belief among experts in the field that it was notfeasible to capture carbon dioxide directly from the atmosphere becauseof the low concentration of that compound. It was subsequently shown bythe copending prior application that it was in fact practical andefficient to carry out such CO₂ reductions under specified conditions.

It was shown that under ambient conditions CO₂ can be efficientlyextracted from the air using a suitable regenerable sorbent system and alow temperature stripping or regeneration process.

SUMMARY OF THE PRESENT INVENTION

The present invention provides further new and useful systems andmethods for removing carbon dioxide from a mass of carbon dioxide ladenair.

This invention has now been further improved by the discovery that thesame low temperature system can also be applied to the capturing of CO₂from a mixture of gases having enhanced carbon dioxide concentration byadmixing air with relatively concentrated CO₂-containing, flue derivedgases diluted with a predominant amount of ambient air; as a furthersurprise, this further improves efficiency. This can result in aCO₂-negative system event for such otherwise “dirty” sources such aspower plants, or refineries, or cement manufacturing plants. In suchcircumstances, it is usually preferable to pre-treat the flue gas toremove particulates and certain destructive compounds, such as sulfurand nitrogen oxide compounds, before contacting the carbon dioxidesorbent, for example where the gas is derived from the burning of coal.

Generally, with extraction directly from the atmosphere, and thecapability to increase the concentration of carbon dioxide in theambient air being treated, by admixing with a high CO₂-content gasmixture, such as flue-originated gases, one can reduce previouslyexisting CO₂ concentrations, in the atmosphere, thus providing acombined carbon-negative process, and compensate for other greenhousegases, such as methane, being added to the atmosphere that may otherwiseincrease their concentrations. It is now possible to thus reduce, oreven reverse, climate change.

In our earlier work, it was realized that a highly efficient system forremoving CO₂ from the relatively low concentration in ambient air couldbe achieved without requiring significant energy use to regenerate theCO₂-loaded sorbent, using saturated process steam. It has now been foundthat an improved result is obtained by utilizing an array of therelatively thin, large surface area, monolithic, porous substrate, asthe support for the active sorbent sites, in tandem with each other. Forsuch a system, substantial quantities of flue-originated gases can bemixed with the ambient air, to increase the concentration of CO₂ in theair being treated, by an order of magnitude, and possibly even more,while continuing to improve upon the low temperature efficiencypreviously achieved for ambient air alone, by varying the conditions andoperating in tandem with another monolith system.

In such an improved system, the tandem pairs are phased such that whenone of the pair is completing being regenerated in its regeneration box,the second member is just entering its regeneration box. The secondregeneration box is sealed, as described in the copending applicationand again below, and the trapped atmosphere is exhausted from the secondregeneration box, to below 0.4 BarA, and preferably below 0.3 BarA andoptimally down to between 0.1 and 0.2 BarA. The first regeneration box,which had also had its air exhausted, has been regenerated withsaturated steam, which condensed within the pores of the monolith as theCO₂ was stripped from the sorbent. When regeneration had reached itsdesired endpoint, the monolith contained hot, condensed water and thesurrounding atmosphere in the sealed box, containing some steam vaporand remaining CO₂, had been increased to at least about 0.7 BarA. Theinteriors of the two tandem regeneration boxes are then interconnected,so that there is a sharp, quick change in the pressures towardsequalization; the hot condensed water in the first monolith is vaporizedat the lower pressure, and when the vapor encounters the secondmonolith, that is warmed and some CO₂ is released, while the vaporcondenses on the second monolith; thus quickly cooling the firstmonolith and preparing it for movement out of the first Box and intocontact with the CO₂-laden gas mixture. This tandem operation iscontinued for all members of the array in order to achieve asubstantially continuous treatment of the CO₂-laden gas mixture, andcontinuously repeated.

It must be understood that a ‘porous substrate’ is one having openpores, where a gas or vapor can enter a pore at the front surface andexit from the rear surface, so that the gas or vapor can pass fullythrough the substrate thickness via the open pores. The thickness of themonolith is preferably at least an order of magnitude less than eitherof the dimensions of the monolith surface transverse to the direction offlow of the CO₂-laden gas mixture to be treated.

The term “ambient air”, as used in this specification, means andincludes unenclosed air under the conditions and concentrations ofmaterials present in the atmosphere at a particular geographic location.The term “flue-originated gases” refers to gases containing a highconcentration of CO₂ and exiting from the combustion ofcarbon-containing materials, such as so-called fossil fuels, includinggases which may have been pre-treated after exhausting from the point ofcombustion.

It has been found that this process is successful with almost anyadmixture with ambient air that comprises at least a predominantquantity of ambient air, by volume, to dilute the flue-originated gases.The flue-originated gases will greatly increase the concentration of CO₂in the mixture, as compared with the ambient air, and are fully mixedinto the air by a system, for example, as shown in FIGS. 25 and 26 ofthe prior copending application, to form a substantially uniform, highCO₂-content gas mixture.

The CO₂ laden gas mixture, at ambient temperature, is treated bydirecting it through a sorbent structure comprising a relatively thin,high surface area, porous monolith, supporting active CO₂-sorbent sites,that can bind (capture) CO₂, and then regenerating the sorbent bycausing the release of the sorbent CO₂ from the sorbent, by treating thesorbent structure with low temperature, preferably saturated, processsteam, at a temperature of not greater than about 120° C., andwithdrawing the released CO₂ (thereby effectively regenerating thesorbent structure) and obtaining high quality CO₂. The sorbentpreferably exothermically adsorbs the CO₂ which allows for therelatively low temperature stripping of the CO₂ from the sorbent.

In this application, the substrate structure preferably comprises anamine that binds to CO₂, and which is carried by the substratestructure. The sorbent will be preferably held on the surfaces of thesubstrate, including the surfaces within the pores. It was previouslythought that when carbon dioxide concentration was much above that ofambient air, the CO₂ sorbent temperature would be too high due to theexothermic heat from the adsorption of the CO₂, which would raise thetemperature of the monolith. It is known that the effectiveness of thesorbent, in the presence of air, would be degraded, at such highertemperatures. It was expected the effectiveness for capturing CO₂, wouldbe diminished, and would require a higher temperature to regenerate thesorbent.

It is known that the fraction captured by adsorption depends upon thetemperature of the exothermic sorbent, in a way given by its Langmuirisotherm; for the available primary amine sorbents. The isotherm isexponential with temperature, because of the adsorbent's high heat ofreaction with CO₂, i.e., about 84 kj/mole. For example, a temperatureincrease from 25° C. to 35° C. reduces the percent of amine sites thatcan capture CO₂, at equilibrium, by about e⁻¹. As a result, the ambienttemperature in cold weather, i.e., winter in the mid or higher latitudesor elevations, reduces this problem, or allows a higher concentration ofCO₂ to be treated. For example, if the ambient temperature is 15° C., arise of 10° C. would yield the same performance as the 25° C. caseambient location treating a lower concentration of CO₂. The Langmuirisotherm for a primary amine is close to optimal at about 15° C. interms of the fraction of amine sites in equilibrium and the sensibleheat needed to strip and collect CO₂ from the sorbent, so as toregenerate the sorbent effectively at about 100° C. A conceptual designis shown in FIG. 27 of the prior copending application, where theeffluent gas is fully mixed with the air through a suitable apparatus,and the temperature rise is analyzed.

A particularly efficient embodiment of this invention is achieved if itis integrated into a CO₂ generating process, such as a power plant,which includes a prior art treatment process, which at the least removesparticulates and sorbent poisons, such as oxides of sulfur and nitrogen.Generally, most coal-burning plants in North America or Europe provide apost-combustion treatment using a process generally referred to as CSStechnologies. One generally used such process is the so-called“post-combustion MEA process”, as practiced by the Costain Group PLC, ofEngland, and as shown diagrammatically in FIG. 3, showing its use in acoal fired power plant, and its treated effluent being passed to theprocess of the present invention. The effluent from the CSS Process,which is free of particulates and the usual poisons of the sorbent usedin the process of the present invention, is admixed with ambient air fortreating with the present process to capture the combined CO₂. Theincremental cost per tonne of CO₂ removal by the CSS Process increasessharply as one increases the percent of CO₂ removed from the gas mixtureand becomes very costly as one goes from 90% to 95% removal. On theother hand, as one reduces the percent captured by the CSS Process,alone, it often becomes costly because the penalty for the CO₂ notcaptured increases in situations where CO₂ emissions are regulated, thusreducing the value of the whole process. For these reasons the targetfor CSS is usually 90%.

On the other hand, the costs per unit amount of pure CO₂ captured by theprocess of the present invention are reduced as the percent of CO₂ inthe process stream entering the process of the present inventionincreases; this is especially effective when combined with the effluentfrom such a CSS Process, or other flue gas pretreatment. As theconcentration of CO₂ in the feed stream increases, however, the processof the present invention must provide the necessary cooling means toinsure that the temperature rise from the exothermic capture of themixed CO₂ does not cause the degradation of the effectiveness of thesorbent. There is thus an opportunity to optimize the cost per tonne ofCO₂ captured by calibrating the relative effect of the combination ofthe CSS Process and the present invention by reducing the percent of CO₂removed in the CSS stage—say if one backs off to 80% removal of CO₂ inthe prior art CSS Process, and mixing the remaining relatively high CO₂content CSS effluent (containing, e.g., 2% CO₂) with ambient air. Inthat case, for every 1% of that CSS effluent stream one mixed with theair, one would increase by about 50% the CO₂ concentration in the feedgas mixture into the process of the present invention.

The associated temperature rises can be determined, because thetemperature rise depends on the rate of CO₂ adsorption and thus theconcentration of CO₂ in the mixed process feed stream. If one mixed in5% of the CSS effluent, it would reduce the capital costs for theprocess of the present invention by a factor of 3 (because theconcentration is three (3) times higher in the mixed stream than in theair alone) over a stand-alone pure ambient air capture process. Thetemperature rise for that case is close to the rise when mixing the fullflue gas stream version of the carburetor, or about 3.5° C. Mostimportantly, if the air capture process of the present invention wereset to remove only 70% of the CO₂ from the mixed stream, the combinedprocesses would remove over 100% of the CO₂ emitted by the power plant.It would thus produce carbon-free, or carbon-negative, electrical poweror other product, having used the burning of fossil fuel as the energysource. In removing 75-80% of the CO₂, by the process of the presentinvention, from the mixed gases, the result would be a carbon-negativepower-generating process.

Besides achieving direct benefits from reducing the cost per tonne ofCO₂ collected, by having each process optimizing the cost of the other,there are also other benefits from process integration. These benefitsinclude that the exhaust stream from the flue gas processing is clean,removing that problem/cost for the mixing step, and more efficient andlower cost use of energy. There are many different pre-combustion andpost combustion CO₂ removal processes being pursued, other than the CSSProcess, and new ones could well emerge in the future. The details ofthe amount mixed of the ambient air and the CSS effluent, and possibleadditional processing of the exhaust from the first stage flue gasprocess, will vary in detail but the basic advantages of the combinedprocess remain qualitatively the same.

To allow for the capture from a higher concentration of CO₂, the presentadvance is based upon the discovery that allowing condensed steam, aswater, to remain in the monolith pores after the stripping of the CO₂ iscompleted, rapid evaporation of a portion of the hot condensate liquidis a highly useful tool to rapidly cool the monolith. The stripped,cooled monolith is then returned to the CO₂-capture station and for afurther sorption step, while conserving the heat by preheating theCO₂-loaded sorbent preliminarily to stripping. The monolith and sorbentwould otherwise be undesirably heated during the sorption step, and thuswould be more susceptible to degradation when exposed to the CO₂-ladenair. This effect is most readily achieved in a monolith having athickness, or length in the direction of the incoming air flow, ofpreferably not more than 10% of the largest other dimension of themonolith, e.g., a thickness of fifteen (15) centimeters, and a length orwidth of at least two (2) meters, by 0.5 meters, i.e., a surface area,transverse to air flow, of at least 1 meter square.

The rate of cooling the regenerated substrate can also be improved bypumping the regeneration box pressure down, e.g., preferably to lessthan 0.3 BarA, and most preferably to between 0.1 and 0.2 BarA, toremove most of the air before starting the flow of process steam throughthe substrate. This will also enhance the efficiency of the removal ofhigh purity CO₂ by eliminating most non-condensable gas before thestripping of the CO₂.

In one of its basic aspects, this invention provides additionalstructures and techniques for capturing carbon dioxide from carbondioxide laden air, and using process heat to separate carbon dioxidefrom a sorbent and regenerate the sorbent.

Moreover, in another of its aspects, this invention provides someadditional structures and techniques that allow the efficient capture ofcarbon dioxide from higher concentrations of carbon dioxide in air,without forfeiting the use of low temperature process heat to separatethe carbon dioxide from the sorbent and regenerate the sorbent. Thisinvention further allows the capture, by sorption, of carbon dioxidefrom admixtures of air with flue gas and separation and regeneration.This allows a CO₂-generating primary system to be rendered netCO₂-negative, and thus reduce the amount of CO₂ in the atmosphere.

In addition, this invention provides a relatively low cost andrelatively pure source of CO₂ for such beneficial uses as feeding algaefarms for biofuel production, where the capture costs represents theentire cost of the CO₂ supply.

In another embodiment, intended to further improve the performance andefficiency of the system, the regeneration chamber box is constructed sothat the back wall (the gas collection side-opposite to the steaminjection side) of the regeneration Box 3051 acts as a condenser of anysteam passing through the monolith as vapor. If the wall is cooled bycirculating water or has enough thermal mass to remove the heat, andthen be cooled by air, than the steam will condense on the cool surface,forming water, by transferring its latent heat to the wall. Additionalsavings are achieved by eliminating an additional heat exchanger. If theback wall is kept at 40° C. or below, by cooling its thermal mass, thenthe back wall will function as a pump, by reducing the temperature inthe closed regeneration box. The inner surface of the back wall can beprovided with downwardly slanted ribs, to direct the condensed water tothe side edges of the box, so as to prevent a large build up ofcondensed water on the back wall; such a buildup would slow the cooling.Such a system provides an efficient way to cool the monoliths for thefollowing reasons: 1) it can be done quickly; 2) no additional capitalexpense is required for separate condenser; and 3) no need to pump watervapor for evaporative cooling, saving a lot of energy.

Although the processes of the present invention are best utilized incolder climates, in order to optimize the effective regeneration of thesorbent, while limiting any potential loss of effectiveness, thedifficulty is that in the coldest climates, i.e., at the highestlatitudes, there are very few preexisting plant facilities to which toattach the CO₂ capture process. It has been realized now, however, thatdue to the greater efficiencies at such locations there is a basis toprovide a stand-alone plant where there are no other facilities toprovide either enhanced CO₂ concentration or to provide the necessaryprocess heat. A system, in accordance with this embodiment, provides astand-alone unit which has no accessibility to external process heat orelectricity and exists in a colder climate having extremely lowtemperatures such as the arctic region. The lower the temperature,substantially without limits, will result in a more efficient operatingsystem. As the system is wholly contained, even conditions in an areasuch as in the Arctic, susceptible to extreme cold and frozenprecipitation, should not interfere with the operation of this system.This will be especially true where the system is operating adjacent toor near a long distance pipeline carrying, for example, crude oil ornatural gas from, e.g., the far North, to those areas of humanhabitation where it would generally be more likely useful.

In accordance with one embodiment of the present invention, a systemincluding a generator of heat such as a boiler is connected to anelectrical generator to operate the necessary auxiliary systems, e.g.,an elevator system, the necessary control devices, valves, andcompressor pumps, for the highly pure CO₂. The high temperature heat isused to generate high pressure steam to operate the electricalgenerators, and the flue gas exhaust is utilized by admixing withambient air so as to proceed in accordance with the earlier-describedsystem. In this manner, the heat and other energy is provided to operatethe system and, for no additional cost, the ambient air is furtherenriched by CO₂, so as to allow for a more efficient capture of thecombined CO₂. Such a system can be almost revenue neutral (but almostalways CO₂-negative) even where there are energy costs, as long as thereis a market or a use for the pure CO₂ that is generated. For example, inthe circumstance of a long distance pipeline, the purified CO₂ can be atleast partially stored adjacent the pipeline. In the event of anyaccidental fire or leakage, the CO₂ can be used to snuff out most blazesthat can erupt.

It is noted that there may be situations where the value of the purifiedCO₂ is in fact greater than the cost of the fuel for the electricitygeneration at a particular location. In that circumstance, for exampleimmediately adjacent a pipeline or a high latitude natural gas well, themore energy that is used and the more flue gas generated, the greaterthe value of the ultimate process for the generation of the pure carbondioxide. In this case, the greater surprise happens where it is morevaluable to use as much energy as possible and thus generating more CO₂,rather than to conserve energy in what would be a more common situation.It is unlikely that such a situation would ever exist outside of thehigher latitude, but, in that case (such as winters in mid-latitudes),this embodiment would be of great utility.

The substrate for the sorbent can be a monolith, formed, for example, ofa silica material, such as cordierite, or an alumina structure, or froma polymeric material having intrinsic adsorption sites, such as apolymer having primary amine side groups. Generally the cordieritemonolith would be expected to require more heat than the aluminasubstrate. In the situation where the CO₂ has the enhanced value, agreater profit would then be made.

In operation, a system embodying this energy enhanced process will use ahigh temperature heat source and micro turbine to generate the necessaryelectricity. The lower temperature heat discharged from the turbine willbe used to regenerate the CO₂ sorbent. The feed stock to the CO₂ sorbentwould comprise a mixture of ambient air plus the exhaust from the heatsource. Where the heat source is natural gas there might be very littlenecessity to pre-treat the exhaust before feeding into the adsorber.However, if coal or fuel oil is used, some initial mitigatingpre-treatment would be necessary in order to remove particulatematerial, which would otherwise clog the substrate pores, as well as toremove certain by-products such as sulfur and nitrous oxide, which mightotherwise poison the sorbent.

In computing the cost effectiveness of any system of this invention, thefollowing equations can be utilized, where

     CE/T  equals  Cost  of  Energy  Per  Ton  of  CO₂$\mspace{79mu} {{{{CE}/{MMBTU}}\mspace{14mu} {equals}\mspace{14mu} {Cost}\mspace{14mu} {of}\mspace{14mu} {Energy}\mspace{14mu} {Per}\mspace{14mu} {Million}\mspace{14mu} {BTU}},\mspace{14mu} {\mspace{76mu} \;}{i.e.},\; {1.055 \times 10^{9}\mspace{11mu} {joules}\mspace{14mu} \times \frac{1}{CE}}}$E/T  equals  Energy  Needed  Per  Ton  of  CO₂, measured  in  MMBTUCO₂/MMBTU  equals  quantity  of  CO₂  emitted  per  million  BTU.     REV  equals  revenue  per  ton  of  CO₂

When computing the operational costs of the system, the capital costs ofthe boiler and electrical generation shall be ignored and it will beassumed that there is no extra capital expense for the fuel generatedCO₂, just the cost for the fuel. Assuming the case of SH/HR equals 1.2,which translates into E/T equals 4 MMBTU and REV equals $40.00 per tonfor natural gas, CE/MMBTU equals $3.00; CO₂/MMBTU equals 53 kg so thatCE/T equals 4×3 minus 40×4×0.053 equals $3.50 per ton.

For coal, on the other hand, the cost of energy per million BTU ishighly variable but can be assumed equal to $2.50; the CO₂/MMBTU equalsagain 0.092 so that the CE/T equals 4×$2.50 minus 40×4×0.092 equals$7.60 per ton. Interestingly, the cost of electricity would be equal tothe percentage of CO₂ added from the flue, i.e., 21% in the case ofnatural gas and 37% in the case of coal.

Further, for remote locations for EOR and merchant gas markets, revenueshould be far greater than $40.00 per ton, thus further reducing the netcost of any energy provided, assuming that the marginal cost forproducing the additional CO₂ is low. By utilizing the high temperatureenergy to produce electricity and the process heat to strip CO₂ from thesorbent, the economics become extremely favorable.

These and other features of this invention are described in, or areapparent from, the following detailed description, and the accompanyingdrawings.

BRIEF DESCRIPTION OF THE FIGURES AND EXHIBITS

FIG. 1 is a block diagram of a system for removing carbon dioxide fromthe atmosphere according to an exemplary embodiment of this invention;

FIG. 2 is a map illustrating a global system of multiple units, suitablefor acting as a global climate modification system, according to anexemplary embodiment of the present invention;

FIG. 3 is a schematic illustration of a prior art pre-treatment systemfor flue gases, and connected into this system of this invention;

FIG. 4 schematically illustrate the preferred tandem version of a systemand technique for removing carbon dioxide from carbon dioxide laden air,and regenerating the sorbent that absorbs or binds the carbon dioxide,according to the principles of the present invention; where AbsorptionTime is approximately equal to Regeneration Time to achieve the greatestefficiency;

FIG. 5 is a schematic illustration of a vertical version of a monolithmedium for removing carbon dioxide from an atmosphere and for removingcarbon dioxide from the medium, utilizing a vertical motion system orelevator to move the monolith between the upper air contact position(where the air movement is aided by a mechanical blower) and the lowerregeneration position;

FIG. 6 is a schematic illustration of a horizontal version of a monolithmedium for removing carbon dioxide from an atmosphere and for removingcarbon dioxide from the medium, utilizing a horizontal track; and

FIG. 7 schematically shows a cut-away side view of one of the tandemsystems elevator structures of FIG. 4, showing the monolith in theregeneration chamber.

FIG. 8 is a schematic illustration of a carbon dioxide removal system,originally shown in the incorporated prior application Ser. No.13/098,370, showing one of the added tandem pairs of carbon dioxideremoval structures forming a part of the present invention.

DETAILED DESCRIPTION OF INVENTION

Background Description of the System and Method Concepts of applicationSer. No. 13/098,370

Following the system shown in the copending application (U.S. PatentPublication 2011/0296872), the following preferred embodiments of thepresent invention have been found to allow for the treatment of morehighly concentrated gas mixtures of CO₂. By following the processdescribed herein, ensuring that the substrate meets the requirements setforth in this description, a concentrated CO₂ mixture can besuccessfully treated, efficiently and at low cost, so that not only arethe greenhouse gases from, e.g., a power plant, completely removed fromthe atmosphere, but the present process will result in a netcarbon-negative effect, withdrawing more CO₂ from the atmosphere thanthe plant emissions, and thus resulting in an overall reduction of CO₂in the atmosphere.

CO₂ laden air is passed through the sorbent structure, which ispreferably shaped so that the dimension in the direction of the air flowis much smaller, e.g., at least one and preferably at least two ordersof magnitude smaller than the other two dimensions defining the surfacesfacing in the path of the air flow. The CO₂ binding sites on thesurfaces of the substrate structure, e.g., primary amine sites, must beable to spontaneously bind the CO₂, usually meaning that it is anexothermic reaction at ambient conditions, until the sorbent structurereaches close to the saturation level; this can be determined, forexample, by measuring the concentration of CO₂ of the air exiting thesorbent structure, known as the breakthrough amount.

When the desired CO₂ breakthrough amount is reached, the sorbentstructure is removed from the carbon dioxide laden air stream andisolated from the atmosphere, in a sealed regeneration chamber, and theCO₂ is stripped off and the sorbent structure regenerated, in a mannerdescribed further below, by being exposed to process heat in the form oflow temperature, saturated (at ambient pressure) steam passed throughthe sorbent structure. The steam will initially condense and transferits latent heat of condensation to the sorbent structure, heating thestructure until the temperature is reached at which the CO₂ is strippedfrom the adsorbent sites and is pushed out of the substrate structure bythe steam, as it passes from and through the front part of the sorbentstructure until the entire sorbent structure will reach a uniformelevated saturation temperature. As the steam contacts and heats thesorbent, it condenses on the monolith, for each approximately two (2)moles of steam that condenses it provides sufficient latent heat neededto liberate, or strip, one (1) mole of the CO₂ from the primary aminesorbent and push out the CO₂ from the sorbent structure; an exhaustfan/pump can also be used to collect and remove CO₂ from theregeneration chamber, as the CO₂ is stripped off. This technique isreferred to as “steam stripping” and is also described further below.For energy efficiency and cost reasons, it is desirable to minimize theamount of steam used and that is mixed in with the CO₂ effluent, and toreclaim the hot condensate to be reheated to steam. Thus, whatever is(or can be) condensed, upon exiting the regeneration chamber, thecondensate can be added to that generated in the regeneration chamber,and recycled to be heated and converted back into steam for further use.

The stripping process usually will be terminated at the onset of steambreakthrough, when the amount of uncondensed steam emerging from thebackend of the sorbent structure becomes large compared to the newlystripped CO₂. The exact conditions for terminating the injection of newsteam will be determined by balancing the increased fraction of CO₂removed with the increased cost of energy as the steam process becomesless efficient in terms of the ratio of CO₂ liberated per quantity ofsteam used. That energy needs to be replaced when the steam andcondensate are reheated for the next stripping cycle, i.e., the energyrequirement to maintain the equality of the CO₂-capture time and theCO₂-stripping and cooling time.

The System

In designing the structure of the system incorporating the presentinvention to be commercialized, the following design parameters shouldbe considered. In general as one increases the loading of the sorbentsites on the substrate, one also wants high amine efficiency as definedby the fraction of amine sites present that are available to bind theCO₂. This is the reason for preferring primary amines and also foradjusting the loading so as to minimize pore blockage by excess sorbent.Experimental results indicate that the optimum loading that balancesamine efficiency with increased loading is between 40-60% by volumeorganic amine content relative to the porous substrate/skeleton to whichit is attached or onto whose pore surfaces it is deposited. This can bedetermined by the following calculation, where:

-   -   Pcm=Density of the skeleton material (e.g., silica or alumina),        in kg/cubic meter    -   PORc=Porosity, the ratio of the open wall area to the total        surface area perpendicular to the direction of air flow    -   PUR=Ratio of CO₂ released to trapped air, purity of CO₂,    -   RH=heat of reaction;    -   SH/RH=Ratio of sensible heat to heat of reaction RH during        regeneration    -   Savc=Surface area per volume of the skeleton, in 1/meters        squared of surface/meters cubed    -   SH=sensible heat    -   TA=Time to fill to saturation with CO₂, time for adsorption,    -   TS=Time to regenerate using steam stripping,    -   w=skeleton pore wall thickness    -   d=average pore/channel size        These are important design parameters to be considered in the        design of this process. In this model, for ease of calculation,        PORc is equal to the ratio of the average open channel area to        the total average area, ignoring the tortuous nature of the        curves in the channels of the walls of the porous medium. Thus,        PORc=d²/(d+w)². The surface area per volume is given by Savc=4        d/(d+w)²=4 PORc/d. The pressure drop is dependent upon the size        of the openings in the channel, the void fraction of the        monolith, length and velocity of air flow through the pores.

Sorbent Structure and General Operation of Sorbent

One example of a type of substrate that can be used is a silicamonolith, produced by Corning, under the trademark CELCOR®. Thatmonolith can be used as the support for a sorbent structure, inaccordance with the principles of the present invention. The sorbent(e.g., a primary amine, such as) is carried by (e.g., coated orotherwise immobilized on) the inside of one or more of the CELCOR®,cellular ceramic substrates, which provides a high surface area and lowpressure drop, as CO₂ laden air flows through the substrate. The sorbentmonolith structure can comprise, e.g., a plurality of the CELCOR®cellular, ceramic substrates, stacked as bricks, or a single monolithicsubstrate, described for example in connection with the copendingapplications. Other examples include the substrate and sorbent disclosedin published application US2011/0179948, or as described in a journalarticle by Choi et al, Amine-Tethered Solid Adsorbents Coupling HighAdsorption Capacity and Regenerability for CO₂ Capture From Ambient Air,by Sunho Choi et al, CHEMSUSCHEM 2011, 4, 628-635 (2011 Wiley-VCH VerlagGmbH& Co. KGaA, Weinheim).

The CO₂ laden air is directed through the pores of the sorbentstructure. It is also contemplated that the sorbent structure can beformed by embedding the sorbent material in an, e.g., alumina coating onthe walls of the CELCOR® cellular, ceramic structure to form amonolithic sorbent structure.

It is also noted that an even more preferred structure is formed ofbricks of porous alumina, in place of the silica of cordierite. Althoughthe alumina structure is not physically and/or thermally as robust asthe silica structure, the less rigorous conditions met in this ambienttemperature capture process, and relatively low temperature strippingprocess, allow the use of the less robust structure. In addition, itshould be noted that the substrate, in addition to the above ceramicstructures, inorganic materials, the sorbent structure can be an organicmaterial such as is formed from a polymerized polyamine by cross-linkingthe amine polymer to form a solid polymer, the solid polymer should becapable of being extruded at low enough temperature that the polymerdoes not volatilize, nor be softened at the temperature of the strippingsteam, i.e., at up to 120° C., used for regeneration of the sorbent.

In general as one increases the loading one also wants high amineefficiency as defined by the fraction of amine sites present that areavailable to bind the CO₂. This is the reason for preferring primaryamines and also for adjusting the loading so as to minimize poreblockage. Experimental results indicate that the optimum loading thatbalances amine efficiency with increased loading is between 40-60% byvolume organic amine content relative to the porous substrate/skeletonto which it is attached or into whose pores it is deposited.

If Ns is the number of CO₂ binding sites per square meter of poresurface, Av is Avogadro's number, and if the density of the material ofthe skeletal structure is Pcm, the porous skeleton will have a densityPc given by Pc=(1−PORc) Pcm; then the loading L in moles per kilogram ofsorbent structure is given by

L=NsSavc/AvPc=4NsPORc/AvdPcm(1−PORc)

If one solves the above expression for PORc, one finds

L=(4Ns/AvPcm)(1/(2w+w2/d))

Since it is desirable to maximize the loading of CO₂ adsorbed by thestructure, the polyamine sorbents provide the desired high Ns. In anycase the above analysis makes clear that it is preferred to have as thinwalls as possible, between the pores/channels in the porous support. Theloading in moles/kg is to first order, independent of the size of thepores, with the decrease in Savc, as the porosity is increased by makingthe pore size larger, cancelled to first order by the decrease in thedensity of the porous support, Pcm.

One can insert the values for Av and for Pcm of 2,500 Kg/m3 (note:averaging the difference in the values for quartz and fused silica) andconvert Ns to Nsn which is the number of attachment sites per squarenanometer, where

-   -   w and d are in nanometers, to find: L=1.33 (Nsn/w(1+w/2d)        moles/kg, of the skeleton structure. For Nsn=5 sites per square        nanometer and w=2 nanometers, a porosity of about 0.5 results in        a surface area per gram of 400 mm², or 160,000 mm² and L=2.5        moles/kg. of the skeleton structure.

The actual loading capacity of CO₂, as kg/m3 of air input, Ld/a, wherethe thickness of the support wall is We and the length (in the directionof airflow) of the monolith is Lm is given by Ld/a=L(0.044)(Pcm(1−PORc))Savm We Lm, which substituting for L,

Ld/a=(NsSavc/Av Pcm(1−PORc))×(0.044)(Pcm(1−PORc))×Savm×We×Lm;

Ld/a=Ns(0.044)/Av)(Save×Savm×We×Lm), Substituting for Savc,

Ld/a=Ns(0.044)/Av)×(SavmWeLm)×(4/d(1+w/d).sup.2).

In one example, using the Corning 230 cell CELCOR monolith, the poreflow length Lm is 0.146 meter, the surface area per volume of themonolith Savm is about 2000 m2/m3 and the pore wall thickness of themonolith Wm is 0.265 mm., determined from Ld/a=L (0.044 kg/mole) (PcSavm 0.146 Wm), for an amount of CO₂ in kg/m2 area of air input. Ageneral design criteria is to make L and Ld/a as large as possible,constrained by the pressure drop constraint, i.e., limited by the forceof the wind and/or fan array, which is met in the first embodiment ofthe present invention using modeling results for the Savm of the 230cell Corning monolith, and the pore length, in the direction of airflow, of 0.146 m and input air flow velocity of 2.5 m/sec.

The walls of the monolith should have the desired PORc, and number ofattachment sites to provide a high Nsn. Wm is determined based uponoptimizing (minimizing) the pressure drop/Savm, which in turn will beconstrained by a limit of how small one can make Wm to have acceptableloading, based upon other constraints (see below). It should be notedthat L increases as w decreases, and d increases, but Ld/a decreases,with increasing pore size for a fixed w, because as the porosityincreases Pc decreases. In general terms, the optimal design has thesmallest w possible, and a porosity that balances the impact of the poresize on the performance parameters described below. It must beremembered that the amine compound may be impregnated as a liquid in thepores of the monolith as well as, or in lieu of, being supported on thewalls of the pore structure.

Air capture following the present invention, is a relatively mildcondition. This feature of the present invention allows the use of amuch less robust structure for the monolith. In particular this permitsthe use of relatively thin walls made out of material with high porosityon to which sorbent is deposited; one such material is alumina. Thiswill save in cost, using materials that are generally less robust andtherefore less costly to manufacture. To prevent degradation of thesorbent, it is necessary to cool down the regenerated monolith to below70° C. before exposing it to air (oxygen), during the sorption stage.The cool down must be done quickly to maximize the time the monolith isadsorbing CO₂. The large amount of heat (about 10⁹ joules for thecurrent silica system—only about ⅔ as much is required for the aluminacase) that needs to be removed in a short time, i.e., 10 to 20 seconds,in the presence of non-condensables, is very challenging; as a furtherchallenge, economics requires avoiding the need for a large condenserwith fast water flow. Although this could be shared with several units,spreading out its cost, it would have a cost impact and not be thatefficient for heat recovery. In addition, the following solution alsohas positive impacts on steam and water use and CO₂ purity. Furthermore,this concept works for sorbent systems that act in tandem, when usinghigher concentration gas mixtures, but can also be adapted for thesingle sorption systems operating on ambient air only.

In this system, as shown in FIG. 4, sealed Box 3051 contains Monolitharray 3041 that has just completed steam regeneration and CO₂ capture,and has a steam off-pressure of about 0.7 to 0.8 BarA, most of the CO₂having been withdrawn through line 3021, which line has been closed. Atthat time, Box 3052 contains Monolith array 3042, which has been lowered(after sorbing CO₂ from the air mixture) into the regeneration Box 3052,and Box 3052 is being pumped out to lower the pressure in the Box 3052to 0.1 BarA, which allows for a saturated steam temperature of 45° C. Bylowering the box pressure, the ultimate result will be greater purity ofthe CO₂ stripped from the regenerated sorbent because the amount of air,of course, is only 10% of the original 1 BarA atmosphere. The cost topump the box of air down to the desired pressure when using electricityis less than 10% of the cost to move the air at 100 pascals pressuredrop.

An additional amount of steam may be added to Box 3051 to push out mostof the remaining CO₂ in the box using the force of the steam, which alsoforces some additional condensate to collect in the pores of Monolitharray 3041. When Box 3051 is exposed to the low pressure of Box 3052,through the line 3014, any steam and hot condensate in Box 3051 willsuddenly expand and evaporate, creating an initial steam burst into Box3052. The Box 3051 outlet line 3014 (when Box 3051 and Box 3052 reachequilibrium) is closed off and Box 3052 is put into connection with thesteam distributer input pipe 3012. This steam burst from Box 3051, beingadded to Box 3052 condenses on the cooler Monolith array in Box 3052,raising its temperature. The steam burst also serves to quickly coolMonolith array 3041, as the condensate evaporates and any steam expands.The velocity of this initial steam burst from the water evaporating fromBox 3051 Monolith array is designed to reach a velocity of at least 10times faster than the air flow speed, or 0.5 mps. The two connectedboxes, Box 3051 and Box 3052, reach an equilibrium at a temperaturelower than T_(regen)−T_(air)/2, because a portion of the heat will beremoved by the stripped CO₂ from Box 3052.

The connection 3014 between Box 3051 and Box 3052, when the lowertemperature is reached in Box 3051, is then closed and process steam isintroduced through line 3012 into Box 3052 and the pressure is allowedto increase to 0.7-0.8 BarA, the process steam strips the CO₂ from theMonolith array 3042. The process steam heats the Monolith array to theT_(regen) temperature and, when the collection of CO₂ drops to a lowerrate that signals completion of the regeneration of the sorbent in Box3042. After the initial steam burst from Box 3051, the lower pressure inBox 3051, which resulted from the evaporation of the hot condensed wateron the Monolith array 3041, also quickly reduces the temperature of theMonolith array 3041 to below 70° C., which allows for the introductionof air to further cool the Monolith array 3041 down to its adsorptionoperating temperature, which is substantially the ambient temperature.The cooled Monolith array 3041 is being raised, as it is air-cooled, tothe adsorption position, receiving fresh CO₂ laden air or mixed highconcentration gasses. This cycle is repeated in reverse, as Monolitharray 3042 becomes fully stripped and Monolith array 3041 returns fromthe air capture zone into sealed Box 3051.

In addition to the greatly reduced cooling time, the advantages in waterand heat usage are clear, saving both by at least a factor of 2.Substrates provide a very good heat sink because of their large surfacearea and thin pore walls. The concentrated carbon dioxide and condensedsteam in Box 3052 from Box 3051 is removed from Box 3052 via line 3022to a capture vessel and the valve in line 3022 is closed and steampassed into Box 3052 from line 3012.

Although the present silica-based Monolith array, i.e., cordierite, hassufficient thermal conductivity, an alumina Monolith array will havefurther improved conductivity and, thus, will result in even fastercooling when combined with the evaporation of condensed water in Box3051 and the condensing of the steam burst on Box 3052. It has beenshown that the heat change effect is 10⁹ joules, resulting in cooling ofMonolith array 3041 within 10 seconds to a temperature below 70° C. Thismethod avoids any additional cost for a separate water-cooled condenser,and water, of course, beyond that used for the process steam, isunnecessary.

It is desirable to minimize as much as possible the time during which noCO₂ adsorption is occurring, in either the Monolith array 3041 or Box3042 Monolith array. This is achieved by operating two sets of monolitharrays in tandem, preferably side by side, so that the cycles for thetwo boxes can be placed in phase so that when one is adsorbing, theother is being regenerated, so as to allow the cooling of one to createthe heating of the other, as explained above. This results in theshortest period during which no adsorption is occurring in both monolitharrays, and, in fact, members of the pair are preferably limited toslightly more than 10 seconds, per cycle for the cooling step. Thetreating of a higher concentration CO₂ gas mixture[[,]] can be moresuccessful when this double tandem cycle is in use.

As a further energy and apparatus saving, as shown in FIG. 4, the tandempairs can act as elevator counterweights for each other, thus reducingthe amounts of energy needed for each raising and lowering cycle, whilealso reducing the number of elevator systems, including motors andcounterweights, needed if a more conventional counterweight system wereused. Such a system, however, does require careful equalizing of thetime needed for each of the capturing and stripping cycles, includingheating and cooling of the monolith array, and capturing and strippingof the CO₂.

It has been demonstrated that fossil fuel combustors, especially naturalgas fired co-generation facilities (cogen), can be effectively, butminimally, pretreated to remove some of the CO₂ and any potentiallyblocking or poisonous impurities, with respect to the monolith array ofthe process of this invention. Subsequently, the pretreatment effluentcan be diluted with ambient air, and used as a feed stock to themonolith arrays. Although certain gas-fired burners require only minimalpretreatment to remove problem impurities, in general the flue gas froma coal burning boiler requires extensive pretreatment to removeparticulates and any compounds that may be poisonous to the sorbent orwhich tend to degrade the substrate. In one embodiment, the pretreatedflue gas from the co-generation process is injected into the sorptionsystem of this invention, along with additional ambient air. In thismixing process, the CO₂ concentration in the air is increasedsignificantly (even with a minor proportion of the additional effluentgas), so that the adsorption step can be performed in a shorter periodof time, comparable to that of a regeneration step. In a preferredembodiment, a parallel set of adsorber/regeneration modules operates intandem with the existing facility. That is, one will be adsorbing CO₂while the other is being regenerated, and vice versa. This mimics acontinuous capture of CO₂. The process is represented by two stages, CO₂adsorption and regeneration of, for example, turbine exhaust, asdescribed in FIG. 1 of the accompanying drawings. In a preferred system,two pairs are operated together so that each tethered pair can act ascounter-balances for each other, thereby saving capital costs for theelevators.

In Stage 1, atmospheric air is mixed with co-generated exhaust gas andthe mixture is passed through the CO₂ adsorption module. This processuses a low-cost, high porosity ceramic substrate (monolith) such asthose used in the automotive catalytic converters, e.g., cordierite, asilica product. CO₂ is captured on the solid sorbent which is bonded toand supported by the substrate. The sorbent does not vaporize ordissolve under the operating conditions during both sorption andstripping, or regeneration. Again, the basis for the effectiveness ofthis invention is the operation of both stripping and adsorption atrelatively low temperatures.

As before, Stage 2 provides for the regeneration of the sorbent bystripping the adsorbed CO₂, using low temperature processing (steam) ina separate regeneration chamber, preferably located at an elevationdifferent, preferably lower, than the adsorption housing position. Thisallows for a simple elevator system to move the monolith array adsorbent3041 between the two levels. In developed regions, where land has value,the vertically off-set arrangement has reduced area. In less developedregions, such as the polar areas, a side-by-side arrangement may bepreferred when situations, and sideways movements, e.g., along rails,may preferably be used in place of the elevator.

CO₂ and steam condensate are the only effluents from the Stage 2regenerator. Generally, it has been shown that when operating at thetemperatures set forth herein, the steam condensate liquid hassubstantially no sorbent material removed with it. The process adsorbsCO₂ from ambient air and can produce a relatively pure CO₂ product gasstream suitable for sequestration or, more significantly, for furtherindustrial use. One example of such use is the generation of new fuel byusing CO₂ as a feed material to a biological system. CO₂ captureefficiency has a measure of energy usage and the adsorber parameters aredetermined based upon concentration of CO₂ in the feed stream, and anynaturally available air velocity provided to the adsorption system,i.e., prevailing winds. The efficiency is also further determined by theavailability of saturated, relatively low temperature steam from aco-generation process, for the stripping of the CO₂ from the sorbent andregeneration of the sorbent. By providing a relatively pure CO₂ off gas,the cost of such CO₂ removal is minimized or can even be made profitablewhen the CO₂ is used, for example, to grow algae capable of providingnew fuel, in oil fields for enhanced oil recovery, or other commercialor industrial applications now presented or which become available inthe future. Growing algae for biofuels is expected to be a major profitcenter for using the carbon dioxide product of this process.

Tandem Operation:

As a further improvement to this process it has been found that capitaland energy savings of a significant quantity can be achieved byintegrating adjacent modules of the sorption/regeneration units in orderto optimize the performance of each of the units.

It has been found that the operation and economics of the system can beoptimized by quickly cooling the regenerated monolith to below thetemperature at which it would be degraded in contact with ambient air.Although the specific temperature would depend upon the nature of thesorbent and monolith used, for a cordierite substrate and an aminesorbent, this temperature limit is below 70° C., in order to avoidexcessive degradation of the monolith in the presence of ambient air. Inaddition, this should be accomplished as part of a regime to minimize toas great an extent as possible, the amount of externally provided heatneeded to be added to the process while collecting high purity CO₂removed from the sorbent.

In order to optimize the overall effectiveness of this system, and toobtain an efficiently operating system, the cooling of the monolithafter regeneration must be accomplished very quickly, so that the stepsof CO₂ capture by the sorbent on the monolith can be synchronized withthe regeneration step. Most advantageously, the cool-down shouldpreferably be achieved within no more than about 10 seconds in order tominimize the time when carbon dioxide is not being adsorbed by themonolith. Based upon the present invention, this effect is achievable inaccordance with the use of the following process parameters:

It has been found that by combining the operation of a plurality ofmodules in tandem, a highly efficient system is provided when treating auniform mixture of ambient air with flue-derived gaseous effluents addedso as to increase the concentration of CO₂ in the feed gas several timesabove that found in ambient air. In addition, obtaining the desiredpurity of CO₂ from the stripping step requires that the regeneration boxhave the majority of the air exhausted before the CO₂ is stripped fromthe sorbent. The first array monolith 3041 has just been through acomplete steam regeneration cycle and the carbon dioxide off gaspressure is at about 0.7 to 1 BAR. The second monolith array 3042,operating in tandem, has been lowered into the regeneration chamberafter completing the CO₂ adsorption step and the air in the regenerationchamber 3042 is pumped down to between 0.2 and 0.1 BAR (which provides asteam saturation temperature of between 60° C. and 45° C.,respectively). The air evacuation allows for improved purity of thestripped CO₂ withdrawn from the regeneration chamber after regeneration,and the cost to exhaust the air after the monolith array has entered thechamber and the chamber was sealed, is relatively a small amount ofpower (usually in the form of electricity).

The two tandem arrays are synchronized so that these conditions are met,at T=0. At that point, the outlets from the first regenerated array Box3041 are switched to the input pipe of Box 3042 so that any steamtrapped in Box 3041 and created by the evaporative cooling of themonolith array in Box 3051 is pumped into Box 3042, when line 3014 isopened, resulting from the large pressure differences (0.7-1 to 0.2-0.1BAR), and the steam then condenses on the relatively cool monolith array3042 in Box 3052, raising its temperature as is required forregeneration. In this manner, the heat removed from the first monolitharray, when cooling, is transferred directly to the second monolitharray to provide at least an initial heat to increase its temperature.The steam burst from Box 3051 into Box 3052 is occurring at a fast flowrate, and preferably at a flow rate of at least approximately 0.5 meterper second, in order to achieve the ten second target. The largepressure drop between the two regeneration chambers should make thisfeasible. When the process is completed, the system is at time cool(T_(cool)).

Box 3052 is preferably pumped down to 0.1 BarA, but Box 3051 is shut offfrom Box 3052 when Box 3052 reaches a pressure of 0.15 BarA. This willresult in a desirable reduction of air in Box 3052 and, thus, a furtherimprovement in the purity of the CO₂ ultimately to be removed. After theconnection between Box 3051 and Box 3052 is closed, the steam forregeneration is allowed to enter Box 3052 and initially condenses on themonolith array 3042 which has been pre-warmed to a certain extent. Theadmission of the steam results in a pressure build-up to between about0.7 and 1 BarA, as the CO₂ is removed from the sorbent on the monolitharray and passed into Box 3052 and pushed out by the final steam. Byallowing the pressure in Box 3052 to increase to 0.7 to 1 as a result ofthe CO₂ and steam collection, Box 3052 ends up as did Box 3051, at T=0,which includes the collection of CO₂ as it is removed from the sorbenton the monolith array. The time to reach this point is equal toT_(cool)+T_(collect) (the time to collect the regenerated CO₂).

In the meantime, the cooled monolith array 3041 is exposed to air, andambient temperature, [[ ]] as it is raised to the adsorption position.The time for monolith array 3041 to return to the adsorption positionequals T_(cool) (the time to cool monolith array 3041)+T_(elevator) (thetime to raise the monolith array to the adsorption position). Monolitharray 3041 is exposed to a flow of air and, over a period of T_(ad),until the adsorption reaches the desired extent, as a percent ofsaturation, or equilibrium. It is noted that, to operate this in themost efficient manner, adsorption does not continue to equilibrium, but,rather, is terminated by removal from the adsorption position at a lowerlevel, generally in the range of 80% to 90% of the equilibrium amount,for the concentration of CO₂ in the feed gas.

To frame this result as a mathematical equation, it can be stated thatT_(cool)+T_(collect2) equals T_(cool)+2T_(elevator)+T_(ad1). It is notedthat T_(collect) and T_(ad) can be independently adjusted in order toreach this desired result. As it is generally desirable to maximizeT_(ad), generally T_(cool) and T_(collect) should be minimized to theextent feasible, and T_(elevator) should be maintained at a low number.

When dealing with the mixed high CO₂ concentration gases, it would bedesirable that the two tandem modules each have two modular arrays andthe two front boxes of each of the tandem modules and the two back boxesof the two tandem modules would be linked so that the cycle of treatingand removing CO₂ from air would be only ½ cycle out of phase with eachother; where ambient air, without added CO₂ is being treated, a tandemdesign is unnecessary but T_(ad) can be as high as ten timesT_(collect), so that if one were to phase ten units, where unit N wouldprovide ½ the sensible heat for unit N+1, in principle, the heat fromN10 could be re-looped back to N1 but the increase in efficiency may notbe sufficient to justify the cost. This type of tandem system results incutting water and heat usage almost in half, and the use of condensersor other cooling aids is omitted, along with the need for separatecooling water.

The monolith substrates provide a large heat sink. As a result of theirlarge surface area, thin porous walls and, in many cases, good thermalconductivity, so as to provide fast cooling by the condensing steam asthe steam passes through the porous monolith.

It has been found that by creating this system of process integration,sorbent lifetime can be increased, heat requirement and water usage canbe reduced, while the purity of the CO₂ product can be increased. It hasalso been found that capital and energy savings are obtained byintegrating neighboring modules. Moreover, it turns out to have asignificant impact on the performance of the individual modules as well.The following three process objectives are, thus, cost effectivelyaddressed:

-   -   Objective 1. To cool the current embodiment, i.e., cordierite,        monolith to below 70° C. before exposing them to air, in order        to prevent degradation. It must be noted that future sorbents        may be more oxygen resistant so that the temperature need not be        reduced quite as much; however, the lower the temperature of the        monolith the faster the CO₂ adsorption.    -   Objective 2. To use as little heat as possible in the process;        and    -   Objective 3. To collect a high purity CO₂.

Objective 1 has become increasingly important because of the need tocool down the monolith very quickly after stripping, as the monolitharrays, in general, have a large amount of sensible heat at that pointin the process. The design target for cooling is 10 seconds, in order tominimize the time spent not adsorbing CO₂. The prior art believed thatseparate condensers were necessary to accomplish this result. However,many options of using condensers have been explored, but, as they allrequire very large surface areas and a great deal of cooling water,because of the large amount of heat and short time allowed for itsremoval, they have not been found to be practical. This is trueregardless of the nature of the monolith substrate that is in use;although cordierite requires the greatest amount of heat removal,another type, for example, an alumina monolith, requires a smalleramount, by a substantial degree. However, even for those types, separatecondensers were not found to be practical. Other adsorbent-supportingmonoliths may require even less heat to be removed, but, in any event,the use of condensers has been shown to be inefficient under almost anyfeasible circumstances.

Objective 2 is also not met by the use of condensers because,transferring heat to cool water, where the water temperature needs to bemaintained at a low temperature for effective heat transfer rate,renders it virtually impossible to economically recover the heat and,thus, cannot reduce the net energy requirements for the system.

Finally, Objective 3 requires that trapped air be removed from theregeneration Box 3052 before collecting CO₂. In addition, by designingthe system for plug flow, so that the evolving CO₂ will push out the airbefore the systems switch to collecting the CO₂, the remaining air isfirst removed from the regeneration chamber. To achieve the targetpurity of at least 95%, a high degree of plug flow is desirable. Plugflow requires that there be no radial concentration differential ofcomponents with temperature and that there be no axial mixing in thedirection of the flow of the gases. This can be achieved when treatingambient air in a single module, or when treating high CO₂ concentratedgas in a tandem module system. The following text only considers twoneighboring tandem molecules to illustrate the process. The processsteps are as follows:

-   -   Box 3051/Monolith array 3041: the monolith array is in the        sealed regeneration Box 3051, and has just completed steam        regeneration and CO₂ collection;—the steam off-pressure is about        0.7-1.0 BarA. This could include introducing some extra steam        after breakthrough to push out any remaining CO₂ (see below).    -   Box 3052/Monolith array 3042 has just been lowered into the        sealed regeneration Box 3052, after capturing CO₂. The Box 3052        is pumped down to 0.2 to 0.1, bar which provides a 60° C. and        45° C., respectively, steam saturation temperature at those        pressures. This evacuation of the air will of course be a big        help to purity of the CO₂ product, because the amount of air is        only 20-10% of ambient air, and the cost to pump one box of air        using electricity is less than 10% the cost to move air at 100        pascals pressure drop, and only 5% in the current embodiment.

Before this process we anticipated only pumping down to cool down afterregeneration and would have had to do it twice if we also wanted to pumpdown for improved purity before regeneration. This integration of twoneighboring modules accomplishes both tasks at the same time with asingle evacuation. One can schedule two neighboring modules, which haveindependent cycles, so they both reach their above described conditionat the same time. One can call this T=0.

Removal of the carbon dioxide and condensed steam from the carbondioxide capture is carried out together with some of the steam andcondensed steam into a separation chamber before Box 3051 output pipe3021 is then switched closed and Box 3051 is opened to the steamdistributor input pipe 3014 from Box 3052, upon completion of strippingand exhausting of CO₂ from the Monolith 3041. The remaining steamtrapped in Box 3051 and created by evaporation (cooling) of monolitharray 3041 is “pumped” into Box 3052 by the large initial differences inpressure (−0.7-1:0.2-0.1 BarA) and condenses on the cool monolith arrayin Box 3052, raising its temperature. So the heat removed from monolitharray 3041 to cool it, is directly transferred to monolith array 3042,to heat it. The velocity of this initial steam burst from the waterevaporating from the monolith array needs to be at least 10 times fasterthan the current 5 cm speed used for steam regeneration, or 0.5 msec, tomeet the 10 second design target. Given the large difference in pressurewhen there is large mass flow and low pressure drop in the monolitharray this should be easy to achieve. The two boxes would reachequilibrium at the saturated vapor temperature of steam at 0.2-0.1 BarA,which is 60-45 C.

To assure that the process is sufficiently fast, it is preferable toreduce the pressure in Box 3052 to 0.1 BarA, but the exit valve from Box3052 is closed at 0.15 BarA. The temperature sought will depend on whatmaximum temperature is the limit to minimize degradation. The pump willhave a check valve on it and will only be pumping after the initial pumpdown if there is a buildup of CO₂ in Box 3052 which is unlikely becauseat the low temperature the partial pressure of CO₂ is lower than 15%which is what 0.15 BarA would represent. So the sorbent will likely keepthe partial pressure of CO₂ below 1 percent. One can adjust this by howmuch of the CO₂ we leave in Box 3051 before we open the valve 3014,which in turn can push out the remaining air further increasing thepurity even before the regeneration process begins. The time for coolingplus switching and transit time of steam=T_(cool): One then closes theconnection 3014 between Boxes 3051 and 3052 and introduces the normalsteam source, through line 3012, into Box 3052; the steam condenses onthe pre-warmed monolith array 3042 and lets the pressure build up to0.7-1 by the presence of CO₂ before beginning CO₂ collection andcomplete the steam regeneration process and collection of CO₂ at theslower rate to complete regeneration of Box 3052-ending up with Box 3052where Box 3051 started. This takes time T_(collect) so total elapsedtime for Box 3052 is T_(cool)+T_(collect).

Cooled Box 3051 is returned to ambient pressure, as the cooled monolitharray 3041 is raised to the adsorption position. It takes a total timeT_(cool)+T_(elevator), and adsorbs for a period of time T_(ad) and thenis lowered for a total elapsed time of T_(cool)+2 T_(elevator)+T_(ad).

To get the two boxes in phase so they can swap their heat back and forthone needs

T _(coo) l+T _(collect) =T _(coo) l+2T _(elevator) +T _(ad)

Since T_(collect) and T_(ad) are independently adjustable this conditioncan be easily met. To maximize T_(ad) one wants to minimize T_(cool) andT_(collect) and have a low T_(elevator). For the case of the carburetorand tandem design, two neighboring modules would each have two modulearrays and one would link the two front boxes from each and the two backboxes so that there is no loss in duty cycle—they would be one halfcycle out of phase with each other.

In the case of air only, a non-tandem design is useful; where the T_(ad)might be 10 times T_(collect) one could in principle phase 10 unitswhere unit n would provide ½ the sensible heat for unit n+1. One couldin principle also reloop the heat from N10 back to N1 but that wouldonly buy you an extra 5% in heat efficiency, with great additional costand complexity.

The advantages of this process in water and heat usage are clear, afactor of close to a reduction by a factor of two for both inputs. Thereis no extra capital cost for a large condenser and no need for anycooling water. The substrates are a great heat sink because of theirlarge surface area and thin walls, and alumina has a good thermalconductivity and thus offers extremely fast “cooling” of the condensingsteam possible.

To demonstrate these advantages, the following calculations illustratesthe basic performance of this system in being able to remove the heatfrom the regenerated monolith array at a sufficient rate to meet the 10second design target utilizing the aforedescribed system. Although theuse of monoliths as heat sinks had previously been recognized, usingthem in this manner, and in the context of this process of CO₂ capturefrom air, has not been known or suggested.

Basic Performance

To operate in the current system, it is necessary to evaporate 22 Kg ofwater/steam from a hot monolith array of 640 individual monoliths tocool the array, such as monolith array 3042, to 55° C. from 110° C. andto condense the evaporated steam, within ten seconds, onto the cool,e.g., monolith array 3041, to prewarm that array. The latent heat ofsteam in this temperature range is 2.3×10⁶ joules so one needs to removeHR=50.6×10⁶ joules in T=ten seconds.

The surface area in a single monolith is quite large. There is 6.4 m² ineach 6 in×6 in×6 in monolith (Nc=230 cell/in², SA=surfacearea/monolith=4 s Nc L FA) where s is opening=1.3 mm, 36.8×10⁴ cells/m²,L=0.15). For a standard unit array of 640 monoliths, e.g., the units3041 or 3042, the total surface area is TSA=4,216 m2.

Thus the thermal flux needed is TFN=HR/TSA=12×10³ joules/m2 in tenseconds, which is quite low; even if any non-condensable gases remain,the steam will condense quickly enough to cool the unit. The only issueis whether heat can be removed fast enough. It is noted that thecondensed water, which tends to limit heat transfer in most condensingsystems, is unlikely to be a significant problem in the heat transfer inthis case. The 22 kg of water occupies 22×10⁻³ m³, which if divided bythe TSA of 4,216 m² yields a water depth of only 0.005 mm, even withoutconsidering that some of the water will be in the pores of the walls.Furthermore at these low temperatures and pressures the sorbent on themonolith itself will remove and immobilize the CO₂, limiting any buildupof concentration of CO₂ in the gas phase.

The thermal conductivity k of alumina is 18 watts/m/° K, but because itis porous assume k=10 watts/m° K. Now the TF, thermal flux/m² in tenseconds in the monolith walls=kT(ΔTemp/w), where w is ½ the wallthickness of the monolith channels. Taking a conservative value for w of0.2 mm, and for ATemp of only 10° K, TF=5×10⁶ joules/m2, which is muchgreater than TFN. The potential performance exceeds the requirements bya sufficient amount that it raises the possibility of doing the CO₂collection at a very fast rate. This could enable a very short cycletime, which could have other benefits. Most notably enabling one to usea short monolith array to capture CO₂ at very high concentrations in thegas mixing case. Alternatively, one could also consider smaller sizedmodule array units for the minor quantities of flue gases, since theirproductivity would be so high.

In the basic embodiment, for treating the monolith array in unit 3051 tocool it down after regeneration and at the same time transfer the heatto the neighboring monolith array in unit 3052, loaded with CO₂, itmight have been assumed that the temperature of the loaded monolitharray was the same as the input feed ambient air flue gas mixture whichhad an 8-fold enhancement in CO₂ concentration. It should be noted insome situations it might be desirable to arrange for the monolith arrayin unit 3052 to heat up due to CO₂ adsorption thus storing the heat ofreaction. For example by reducing condensed water available for coolingduring adsorption; this could raise the overall thermal efficiency ofthe process even more—

-   -   In the base case, one-half the sensible heat could be saved—In        the present case, it would be the sum of ½ the heat of        reaction+½ the sensible heat.        -   One can think of this as increasing the gas mixing heat            efficiency by adjusting its operating Temperature: the            optimum will depend upon the temperature dependence of the            oxidative degradation of the monolith. Generally, the heat            of reaction of the sorbent, and the ratio of sensible heat            to heat of reaction per tonne of CO₂ (e.g., loading and            material and density of monolith walls) will be taken into            account.

Once the concentration non-condensable gases are reduced to a levelneeded to achieve the rate of condensation required, the next challengeis to remove the heat fast enough. As pointed out by Martin andothers—this is both a mass problem (how much coolant-specific heat) anda thermal conductivity problem (how fast can the heat be removed fromthe condensing surface).

In the embodiment of FIG. 8 (taken from the incorporated priorapplication Ser. No. 13/098,370, where only one of the pairs of carbondioxide removal structures is shown but a connection to the secondregeneration chamber 2006A is added) the carbon dioxide removalstructures are moved between the CO₂ capturing zone 2003 and thesealable CO₂ stripping/regeneration chamber 2006. When a substrate ismoved to the CO₂ stripping chamber 2006, i.e., the lower position asshown in FIG. 8, the substrate is at substantially ambient temperaturedue to the cooling effect of the condensed steam in the substrate whenmoved out of the carbon dioxide capture chamber, the heat of reaction ofthe sorption activity having been removed by the evaporative effect ofthe water combined with the convective effect of the blown mass of airfrom which the CO₂ was removed, which is far greater than the amount ofCO₂.

Any trapped air in the substrate 2002 and chamber 2006 can be pumpedout, e.g., by an air evacuation pump 2023, or even by an exhaust fan, toform a partial vacuum in the chamber 2006. Next, process heat, e.g., inthe form of saturated steam from the Steam co-generator 2019, isdirected at and through the CO₂-laden substrate 2002 in the carbondioxide capture chamber 2006.

Carbon dioxide is removed from the sorbent (stripped off) by the flow ofrelatively hot steam; the incoming steam is at a temperature of notgreater than 130° C., and preferably not greater than 120° C., and mostpreferably not greater than 110° C. Under most circumstances a steamtemperature of 100° C. is sufficient. The vapor, comprising primarilycarbon dioxide and some steam, flows out of the carbon dioxide capturechamber 2006, through exhaust conduit 2008 into a separator 3009, whereliquid water is separated as shown and at least some of the steampresent is condensed. The liquid condensed water is separated from thegaseous stripped CO₂. Some of the steam that is condensed in the sorbentstructure itself during the stripping process either will be collectedin a drain at the bottom of the regeneration chamber (e.g., by tippingthe structure slightly off level and pass into container 20) or will beevaporated upon being exposed to the low pressure in the pumped outsecond regeneration chamber 2006A of the pair, after the majority of theCO₂ had been removed to chamber 3009. The condensed water left in theporous substrate structure will be evaporated when the mixed ambient airis passed through the carbon dioxide removal structure during theadsorption step.

The stripped CO₂ from the regenerated sorbent is in turn pumped into astorage reservoir 2012, where it is maintained at slightly elevatedpressure for immediate use, e.g., to provide CO₂-rich atmosphere toenhance algae growth, or the carbon dioxide gas can be compressed tohigher pressures, by means of compressor 2014, for long term storage orto be pipelined to a distant final use, e.g., sequestration or treatingof oil wells or natural gas wells to improve production. During anycompression phase, the CO₂ is further purified by the condensation ofany remaining water vapor, which water condensate is in turn separatedfrom CO₂, by known means.

The idea works for both the tandem which is the preferred embodiment,but can also be adapted for the non-tandem case as well. Box/Monolith 1has completed steam regeneration, and the steam shut-off. Box 3052 hasjust been lowered after adsorbing CO₂, and pumping out of the air fromBox 3052 is beginning, to reduce the pressure in Box 3052 to 0.2 to 0.1BarA. The Box 3051 output pipes are switched to the steam distributorinput pipes of Box 3052; the steam from the evaporating condensed waterin Box 3051 condenses on the relatively cool monolith in Box 3052,raising its temperature. The velocity of this initial steam burst fromthe water evaporating from the monolith needs to be at least 10 timesfaster than the current speed, or 0.5 msec; this will help spread outthe heating but still will have a sharper front than the air case by 5,so no steam will come out the back end. The two boxes will reach anequilibrium at a temperature less than (T_(regen)−T_(air))/2 becausesome of the heat will be taken away by the evaporating CO₂. The 3051connection is then closed and steam is introduced into Box 3052 from thesteam source to complete the heating to T_(regen) and collection of CO₂at a slower rate to complete regeneration of Box 3052. Box 3051containing the cooled monolith array 3041 is then exposed to the ambientair and is raised to the adsorption position.

One process negative is that for a brief time both Box 3051 and Box 3052are not absorbing CO₂ from air. In the case of air capture where theboxes 3051 and 3052 are side by side; the cycles for the two boxes canbe phased so both do not have a reduction in duty cycle. Also in anotherembodiment in the tandem application, if the monoliths were arrangedback to back, than one box would be steam stripping in the directionopposite from the capture direction.

The following invention is claimed:
 1. A method of removing andcapturing concentrated carbon dioxide from carbon dioxide laden air, themethod comprising admixing a first flow of carbon dioxide-laden ambientair with not more than 50% by volume of an effluent gas, where theeffluent gas is derived from a flue gas from the combustion ofhydrocarbons, and directing the first flow of admixed ambient air to afirst carbon dioxide removal structure; the carbon dioxide removalstructure comprising a sorbent supported upon a porous substrate andcapable of exothermically and releasably binding carbon dioxide toremove a predetermined portion of the carbon dioxide from the firstadmixed ambient air mixture; passing the first carbon dioxide removalstructure into a first sealed carbon dioxide capture chamber, exhaustingair from the first sealed capture chamber to reduce the air pressuretherein, and passing steam, at a temperature of not greater than 120° C.into and through the first carbon dioxide removal structure to stripcarbon dioxide from the sorbent and regenerate the sorbent, and removingthe stripped carbon dioxide from the first sealed capture chamber, so asto capture concentrated carbon dioxide; admixing a second flow of carbondioxide-laden ambient air with not more than 50% by volume of aneffluent gas, where the effluent gas is derived from a flue gas from thecombustion of hydrocarbons, and directing the flow of admixed ambientair to a second carbon dioxide removal structure; the second carbondioxide removal structure comprising a sorbent supported upon a poroussubstrate and capable of releasably binding carbon dioxide to remove apredetermined portion of the carbon dioxide from the second admixedambient air mixture; passing the second carbon dioxide removal structureinto a second sealed carbon dioxide capture chamber, exhausting air fromthe second sealed capture chamber to reduce the air pressure therein,and passing steam, at a temperature of not greater than 120° C. into andthrough the second carbon dioxide removal structure to strip carbondioxide from the sorbent and regenerate the sorbent, while the steamcondenses, and removing the stripped carbon dioxide from the secondsealed capture chamber, so as to capture concentrated carbon dioxide;the first and second carbon dioxide removal structures being operated intandem, such that when the first carbon dioxide removal structure hascompleted a regeneration cycle, and the second carbon dioxide removalstructure is prepared to carry out its regeneration, the remaining steamin the first carbon dioxide capture chamber is flashed into the reducedpressure second carbon dioxide capture chamber in order to cool thefirst carbon dioxide removal structure and prewarm the second carbondioxide removal structure prior to regeneration with saturated steam;and the first carbon dioxide removal structure is removed from the firstcapture chamber and moved into a flow of admixed ambient air; passingsaturated steam into the second carbon dioxide capture chamber toregenerate the second carbon dioxide removal structure and removal ofthe carbon dioxide and condensed steam from the second carbon dioxideremoval structure; and repeating the tandem operation so that the firstcarbon dioxide removal structure is returned to the first carbon dioxidecapture chamber after adsorbing carbon dioxide from the flow of admixedair and the pressure in the first carbon dioxide capture chamber isreduced, and opened to the higher pressure in the second carbon dioxidecapture chamber.
 2. The method of claim 1, wherein the carbon dioxideand condensed steam removed from each of the capture structures ispassed to a separation vessel to remove condensed steam as liquid and topass the concentrated carbon dioxide for further processing.
 3. Themethod of claim 2, wherein the carbon dioxide is further processed bybeing compressed sufficiently to remove remaining water vapor to obtainhighly concentrated CO2 of at least 95% purity.
 4. The method of claim1, wherein the pressure in each of the carbon dioxide capture chambersis reduced to not greater than 0.2 BarA.
 5. The method of claim 1,wherein the pressure in each of the carbon dioxide capture chambers isreduced to not greater than 0.15 BarA.
 6. The method of claim 1, whereinthe admixed ambient air contains a concentration of CO₂ at least twoorders of magnitude greater than the concentration of CO₂ in ambientair.
 7. The method of claim 1, wherein the carbon dioxide removalstructure comprises an array of porous substrate monoliths formed of amaterial selected from the group consisting of silica, alumina, andalumina coated silica, and wherein the substrate is supporting an aminesorbent.
 8. The method of claim 7, wherein the sorbent is a primaryamine.
 9. The method of claim 1, wherein the steam is saturated steam.10. The method of claim 9, wherein the saturated steam is process heatsteam.
 11. The method of claim 5, wherein the pressure in each of thecarbon dioxide capture chambers is reduced to 0.1 BarA.
 12. The methodof claim 1, wherein condensed steam remains in the pores of thesubstrate when the regenerated carbon dioxide removal structure isremoved from the capture chamber and moved back into a flow of admixedambient air, so as to serve to moderate the temperature of the sorbentand substrate when adsorbing CO₂ from the admixed air.
 13. The method ofclaim 12, wherein the ambient air is admixed with less than 50% byvolume of the effluent gas.
 14. A system for removing carbon dioxidefrom carbon dioxide laden air, the system comprising a pair of carbondioxide removal structures, each structure comprising a sorbent that iscapable of absorbing or binding to carbon dioxide, to remove carbondioxide from the air, and a porous solid mass substrate upon thesurfaces of which the sorbent is supported, and a movable structuralsupport for the substrate; the structural support supporting the sorbentin a position to be exposed to a flow of carbon dioxide laden air so asto allow for the removal of CO₂ from the air; a pair of sealableCO₂-capture chambers, one for each carbon dioxide removal structure forcapturing carbon dioxide from the CO₂ loaded removal structure; openablefluid connection means between the carbon dioxide capture chamber and anexhaust pump for reducing the atmospheric pressure within the sealedcarbon dioxide capture chamber after the entry of a removal structure;openable fluid connection means between the carbon dioxide capturechamber and a source of process heat steam; openable fluid connectionmeans between the two carbon dioxide capture chambers; and an openablefluid connection means between each carbon dioxide capture chamber and aCO₂ collection chamber; and apparatus for moving a carbon dioxideremoval structure into and out of a carbon dioxide capture chamber. 15.The system as defined in claim 9, wherein the porous solid masscomprises a highly porous monolithic ceramic structure which supportsthe carbon dioxide sorbent to absorb or bind carbon dioxide from theair.
 16. The system of claim 9, comprising a pair of vertically orientedcarbon capture structures, each of which is selectively operable in amanner wherein one of the pair of vertically oriented carbon capturestructures is alternatively and successively in the path of carbondioxide laden air while the other of the pair of vertically orientedcarbon capture structures is being heated with process heat to separatethe previously adsorbed carbon dioxide from the sorbent and regeneratethe sorbent on the porous support.
 17. The system of claim 11, whereinthe vertically oriented carbon capture structure is configured andoperable so that it is alternatively and successively placed in the pathof carbon dioxide laden air, to remove the carbon dioxide from the air,and exposed so as to be heated with process heat, to separate the carbondioxide from the sorbent and regenerate the sorbent.
 18. The system ofclaim 11, comprising an automatically operating valve system designedand adapted to alternatively and successively pass carbon dioxide ladenair to the carbon capture structure and to pass process heat to thecarbon capture structure to separate the carbon dioxide from the sorbentand regenerate the sorbent.